The invention relates to a method for the production of workpieces turned on the peripheral surface on multi-station machine tools, wherein:
rod stock is introduced into a clamping device of the machine tool,
is clamped fast there,
a rod section is cut off at a distance from the clamping device,
the free end protruding from the clamping device is turned.
The invention further relates to a multi-station capstan machine for carrying out the method.
Such a method is carried out with the ordinary multi-station automatic capstan machines which are ordinarily provided with:
a turret or turntable which is stepwise indexable,
a plurality of clamping devices, mounted at circumferential intervals on the turntable, for clamping rod stock from which the turned workpieces are to be produced,
a charging or loading station and a plurality of working stations distributed in the peripheral direction, to which the rod stock clamped fast in the clamping devices can be fed in working sequence by the movement of the turret,
and a cutter device associated with the loading station for the rod stock.
On such automatic machines a rod section is cut off and clamped fast in the clamping device, the length of which section corresponds to the length of the desired workpiece. The clamping devices as a rule are firmly connected with the turret so that as a rule work is carried out on automatic machines with the workpiece stationary and turning tools in rotation. Ordinarily the turret is arranged horizontally and the clamping devices are directed radially so that there is sufficient space for the arrangement of the machining units around the turret. However machines are also known (Ger.Pub.Spl No. 21 02 150) where the turret can move about a horizontal axis of rotation and the clamping devices are oriented axially in relation to this axis of rotation.
One essential advantage of the method for the production of turned parts on turret machines consists in that according to choice it is possible to work rod stock or so-called ring stock (rolled-up rod or wire material) as starting material.
It is disadvantageous that on the known machines turning work on workpieces is possible only on the parts which protrude from the clamping device. At the clamped portion no turning work can be executed. Thus the production of workpieces on such machines is limited as a rule to those parts where the whole peripheral surface does not have to be worked, that is to those parts where there is still a sufficiently large zone left free for clamping. In order to overcome this disadvantage, machines have been constructed in small numbers where the workpiece is firstly turned from one side, then taken out of the clamping device and clamped afresh in a new clamp adapted to the turned diameter, and turned further. This method has the disadvantage that considerable extra expense is necessary for the clamping devices and the workpiece reversing device. Moreover a station is occupied for reversing which otherwise could be used for machining. Furthermore it is disadvantageous that the central axis of the first clamp is practically always offset in relation to the central axis of the second clamp. Moreover with this method the workpieces must often be clamped by such small surfaces that there is danger of the material being distorted by compression at the clamped surface, especially if heavy material-removal takes place in the second clamped position. This leads to corresponding waste.
Workpieces which are to be turned over the whole circumference in one clamped position can hitherto be produced only on single-spindle and multi-spindle automatic rod machines. As known, these work with rotating workpiece. The rod stock is loaded into the spindle drum and advanced by sections through the clamping device in each case, especially a pair of clamping jaws, of the spindle drum so far that it protrudes with its free end by at least one feed length, corresponding to the workpiece length plus the width of a severing tool, from the clamping device. At this free end the clamped-fast rod stock is machined to the desired workpiece shape. The feed of the rod stock is carried out in various ways. In some cases the material rod is grasped on the peripheral surface at the rear end by a retaining gripper and pushed by sections through the clamping jaws, the ejection of the remainder piece taking place to the rear through the retaining gripper. Otherwise a feed gripper is arranged before the clamping gripper of the spindle drum. The material rod is pushed with a push rod through this feed gripper and the clamping gripper, and the feed gripper takes over the further feed movement of the rod by sections. The rod remainder is expelled forward, namely by the next succeeding new material rod. In the case of both types of construction the finished workpiece is cut from the material rod by means of a cutting tool. In the case of the single spindle automatic machine only one workpiece is produced during each machine cycle, the tools come into action in succession. In automatic multi-spindle machines several tools on several spindles are in action at the same time, which is economical in the case of high production figures.
However the single and multi-spindle automatic machines have the following disadvantages in comparison with the automatic turret machines:
expensive spindle halting if operations other than turning are to be executed, for example milling, transverse drilling, transverse thread cutting, riveting, crimping, fitting. These operations can be carried out only with the spindle stationary;
expensive equipment, if work has to be carried out on the workpiece in several longitudinal axes, that is eccentrically of the axis of rotation;
noise nuisance resulting from rotation especially of long material rods of large diameter in their guides;
In the case of automatic multi-spindle machines, very expensive rod-loading devices, if these work fully automatically;
In the case of automatic multi-spindle machines with spindles aligned axially of the axis of rotation of the spindle drum, only a narrow tool space is available, so that tool changing and adjustment are correspondingly difficult.
The invention is based upon the problem of providing a method and an apparatus of the initially mentioned kind so that rod pieces turned on their entire peripheral surface can be produced on multi-station turret machines in one single clamping action. Thus the essential advantage of the automatic multi-spindle machines as regards turning possible over the whole length of the workpiece is to be achieved, but while retaining the essential advantages of the turret machines, namely the possibilities:
of carrying out the whole machining with the workpiece stationary, so that all the connected advantages such as simple execution of eccentric turning work, lower noise nuisance, simpler rod loading devices, are obtained,
in the case of clamping devices aligned radially of the axis of rotation of the turret, of being able to arrange the machining stations more favourably in the radial direction,
of being able to machine material rolled into rings.